What's Perlite Perlite is a volcanic effusive rock whose colour varies between gray and pink, and chemical composition is the same as rhyolites and dacites. Perlite has the capacity to expand its own volume until 20 times since the original when heated at high temperatures, nearly to its softening point. The expansion is due to water confined in the pores of the rock because of the sudden cooling while magma gets out of the volcano.

When heated between 850° and 1000°C, the rocks expandes due to water vaporization: this nonreversible process generates inside the particles many bubbles that brings a unique lightness, special physical properties, especially of themo-insulation, and the typical white colour (Picture 1).

The structure of the particles, clearly visible in some pictures (Pictures 2-5) collected with a scanning electron mycroscope (SEM), is characterized by open pores (small channels that form a thick network) and close pores (isolated cells and holes). The contemporary presence of those cheracteristics gives the rock an extremely high transpiring power (thanks to the open pores) and at the same time high impermeability to water inside the nucleus of the particle (due to the close pores).

Expanded perlite, physically-chemically classifyed as a siliceous glass, is a stable and chemically inert material.

Chemical composition SiO2 74 – 78 % Al2O3 11 – 14 % K2O 2 – 4 % NaO 3 – 6 % Fe2O3 0,5 – 1,5 % CaO 1 - 2 % MgO 0 - 0,5 % H2O di legame 2- 6 %

Physical properties Colour White pH 6,5 – 7,5 Moisture content 0,5 % max Bulk density 35 – 150 kg/mc Softening point 850 – 1100°C Melting point 1250 – 1350 ° C Thermal conductivity (20°C) 0,04 - 0,05 W /mK Calore specifico 837 J / kgK Solubility • Soluble in concentrated alkaline solutions and in HF • Moderataly soluble (< 10%) in NaOH